S-Nitrosylation of DRP1 Does Not Affect Enzymatic Activity and is Not Specific to Alzheimer's Disease

Abstract

Abstract. Mitochondrial dysfunction and synaptic loss are among the earliest events linked to Alzheimer's disease (AD) and might play a causative role in disease onset and progression. The underlying mechanisms of mitochondrial and synaptic dysfunction in AD remain unclear. We previously reported that nitric oxide (NO) triggers persistent mitochondrial fission and causes neuronal cell death. A recent article claimed that S-nitrosylation of dynamin related protein 1 (DRP1) at cysteine 644 causes protein dimerization and increased GTPase activity and is the mechanism responsible for NO-induced mitochondrial fission and neuronal injury in AD, but not in Parkinson's disease (PD). However, this report remains controversial. To resolve the controversy, we investigated the effects of S-nitrosylation on DRP1 structure and function. Contrary to the previous report, S-nitrosylation of DRP1 does not increase GTPase activity or cause dimerization. In fact, DRP1 does not exist as a dimer under native conditions, but rather as a tetramer capable of self-assembly into higher order spiral-and ring-like oligomeric structures after nucleotide binding. S-nitrosylation, as confirmed by the biotin-switch assay, has no impact on DRP1 oligomerization. Importantly, we found no significant difference in S-nitrosylated DRP1 (SNO-DRP1) levels in brains of age-matched normal, AD, or PD patients. We also found that S-nitrosylation is not specific to DRP1 because S-nitrosylated optic atrophy 1 (SNO-OPA1) is present at comparable levels in all human brain samples. Finally, we show that NO triggers DRP1 phosphorylation at serine 616, which results in its activation and recruitment to mitochondria. Our data indicate the mechanism underlying nitrosative stress-induced mitochondrial fragmentation in AD is not DRP1 S-nitrosylation.

Cerium oxide nanoparticles protect against Aβ-induced mitochondrial fragmentation and neuronal cell death

“…14,22 We previously demonstrated that SNOC can trigger DRP1 S616 phosphorylation and mitochondrial fragmentation. 16,21 Furthermore, DRP1 is hyperphosphorylated on S616 in AD patient brains. 21,22 Because nanoceria were able to prevent Ab-induced mitochondrial fragmentation (Figure 4), we next investigated whether they could also inhibit DRP1 S616 phosphorylation, providing a potential mechanistic explanation for the observed mitochondrial preservation.…”

“…16,21 Furthermore, DRP1 is hyperphosphorylated on S616 in AD patient brains. 21,22 Because nanoceria were able to prevent Ab-induced mitochondrial fragmentation (Figure 4), we next investigated whether they could also inhibit DRP1 S616 phosphorylation, providing a potential mechanistic explanation for the observed mitochondrial preservation. Neurons treated with either aged SNOC or nanoceria alone exhibited low baseline DRP1 S616 phosphorylation (Figure 5a).…”

“…A recent report suggested that S-nitrosylation of DRP1 at cysteine 644 increases DRP1 activity and is the cause of peroxynitriteinduced mitochondrial fragmentation in AD; 20 however, the work remains controversial, suggesting that alternative pathways might be involved. 21 For example, peroxynitrite also causes rapid DRP1 S616 phosphorylation that promotes its translocation to mitochondria and organelle division. 21,22 In mitotic cells, DRP1 S616 phosphorylation is mediated by Cdk1/cyclinB1 and synchronizes mitochondrial division with cell division.…”

“…21 For example, peroxynitrite also causes rapid DRP1 S616 phosphorylation that promotes its translocation to mitochondria and organelle division. 21,22 In mitotic cells, DRP1 S616 phosphorylation is mediated by Cdk1/cyclinB1 and synchronizes mitochondrial division with cell division. 23 Interestingly, DRP1 is S616 hyperphosphorylated in AD brains, suggesting that this event might contribute to mitochondrial fragmentation in the disease.…”

“…23 Interestingly, DRP1 is S616 hyperphosphorylated in AD brains, suggesting that this event might contribute to mitochondrial fragmentation in the disease. 21,22 A recent report indicates that Cdk5/p35 is responsible for DRP1 S616 phosphorylation, 24 and notably aberrant Cdk5/p35/p25 signaling is associated with AD pathogenesis. 25 Thus, we explored here the possible role of DRP1 S616 hyperphosphorylation in Ab-and peroxynitrite-mediated mitochondrial fragmentation.…”